2. Pollination experiments were conducted with Serr and Chico trees in the DC

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1 PISTILLATE FLOWER ABSCISSION P.B. Catlin, Gale McGranahan, and D. Voyatzis ABSTRACT Evaluation of the pistillate flower abscission (PFA) potential of UC and UC was continued at two sites. At a high PFA site UC PFA was only moderately lower than Serr for the third year. UC demonstrated low PFA potential for a seconq year at this site. Higher PFA potential of UC than UC was also found at a second site for a second year. No further evaluation of PFA characteristics of these cu1tivars is planned. Preliminary experiments and circumstantial evidence have suggested that excess pollen might cause PFA. Controlled pollinations were carried out with Serr and Chico using two sources of pollen at high and low dosages. Open pollinations and unpo11inated flowers were included. PFA was highest with open pollinations and lowest with unpo1linated flowers for both cu1tivars. With Serr, PFA declined with decreasing pollen load whereas there was no difference with Chico. Pollen source did not affect PFA. Attempts to associated numbers of pollen grains per stigma with normal versus PFA pistils have not been completed. An effect of bagging in reducing PFA may implicate water relations in this phenomenon. OBJECTIVES 1. To evaluate PFA potential in UC-67-l3 and UC To determine the role of pollen in PFA. PROCEDURES 1. In 1990 PFA was determined in the usual fashion by tagging and observation at three to four day intervals (Catlin et a1., 1987) for UC and UC at the same two sites and with the same trees and limbs as in earlier years. 2. Pollination experiments were conducted with Serr and Chico trees in the DC selection block at Davis. Individual shoots bearing one or more reproductive spurs were enclosed in polyester pollination bags with a plastic window on one side. Bags were attached when pistillate flowers had just started to appear and before stigmas were receptive. All catkins and unexpanded buds were removed from the portion of the branches to be enclosed. Pollen of Serr and of (a clone from Iran) was used. Catkins were collected and held one day in the laboratory. Released pollen was screened and stored at -20 C and 33% RH until used. Pistillate flowers inside the bags were pollinated at maximum receptivity (Forde, 1975). Each bag received pollen of Serr or at either 50 or 800 mg per bag. Pollen was inj ected with a syringe previously 87

2 calibrated to deliver the desired amount of pollen. Other bagged branches were not pollinated and a similar set of pistils were tagged but not bagged for determination of natural PFA (open pollinations). Bags were removed days after pollination and the condition of pistils on all reproductive shoots or within the bags was recorded. PFA was identified by pistil size and point of detachment (Catlin et al., 1987). Open pollinated pistils were monitored at 3-4 day intervals from pistil emergence until the fate of all was evident. Treatments were arranged in a randomized complete block design with 42 and 30 bags for each pollination treatment with Serr and Chico respectively. Analysis of var.iance of percent PFA transformed into the arcsin was performed using the SAS computer program. Differences between means were tested with Duncan's Multiple Range test. At the time of maximum receptivity of stigmas an additional batch of open pollinated flowers of similar physiological age were tagged on both Serr and Chico. Pistils from these shoots were removed 10 and 12 days later for pollen grain counts. Pistils were immediately fixed in FAA solution and the ovary diameter for each one was measured. Stigma squashes were prepared (Martin, 1958). Germinated and non-germinated pollen grains on each stigma were counted under UV light in a LEITZ DIAPLAN microscope equipped with an incident light luminescence illuminator. RESULTS AND DISCUSSION Cultivars. PFA was determined for UC-67-l3 (site S, third year) and in a nearby commercial orchard (site F, second year). UC-67-ll was monitored at the same two locations for the second year. At site S, adjacent Serr trees were also monitored. In all cases the same trees and limbs were used as in earlier years. The average PFA obtained in 1990 is given in Table 1. At site S, PFA of Serr was very high, lower for UC-67-l3 and lowest for For each cultivar, levels of abscission were approximately twice as high in 1990 as were found in At site F, PFA for both UC-67-l3 and UC-67-ll was lower than at site S but with UC lower than UC Levels of abscission at site F in 1990 were approximately the same as those found in PFA of UC-67-l3 has been compared versus adjacent trees of Serr at a site where high abscission has occurred in most of 12 years of measurement of this phenomenon. It is concluded that UC-67-l3 can express high PFA at such a site. UC-67-l3 had lower PFA at site F than at site S in one of two years. Although no comparison with Serr was made at site F, low to moderate PFA with Serr was found earlier in the same orchard. UC-67-ll expressed low PFA at both sites in both years of measurement. It is concluded that UC-67-ll is relatively less prone to PFA than the other two cultivars with which it was compared. No further assessment of PFA is planned for UC-67-l3 and UC-67-ll. A manuscript was published reporting PFA characteristics for Serr, Sunland, Chandler, and Howard (Catlin and Olsson, 1990)

3 Pollinatiol}. With Serr, PFA was very high with unbagged, open pollinated flowers (Table 2) and was the same as that found on large limbs on the same trees monitored separately (Table 1). Abscission was lower in bags that received a high pollen dose and still lower with the low pollen load. The source of pollen was without effect. With bagged flowers that did not receive pollen, ovaries enlarged beyond the size (3-4 rom) at which growth stops in PFA. Thus, very little abscission was attributable to PFA in the absence of pollen. Results extend those obtained in 1988 with massive doses of pollen. Similar results were obtained with Chico but with lower PFA of open pollinated flowers and less distinct differences between treatments. The light dose' of of pollen resulted in significantly less PFA than the heavy dose. However, no source or ;imount of pollen caused PFA to differ from the unpollinated control. The difference in PFA between open pollinated Serr and Chico is consistent with the earlier conclusion that Serr can be more seriously affected. The pollen load effect with Serr and its absence in Chico further suggests high sensitivity to causal influences in Serr. Attempts to associate numbers of pollen grains per stigma with normal versus PFA pistils have not been completed. The number of pollen grains per stigma ranged from 29 to 818. With Serr, there were more pollen grains on stigmas of pistils that had stopped growth (PFA type) than on those that had enlarged much beyond the PFA stage (Figure 1). However, intermediate size pistils, currently thought to have grown beyond the PFA stage, had the highest number of pollen grains. With Chico there was no relation between ovary size and pollen grains per stigma (Figure 2). There was an effect of bagging on PFA in addition to the effect of pollination. Condensed moisture was observed inside bags. Thus, phenomenon involving water status or transpirational activities might be involved. Desiccation of stigmas may be related to excessive amounts of pollen. Movement of water and possibly other substances to pistils related to root activities could also be implicated. LITERATURE CITED Catlin, P.B., D.E. Ramos, G.S. Sibbett, W.H. Olson, & E.A. Olsson Pistillate flower abscission of the Persian walnut. HortScience 22: Catlin, P.B. and E.A. Olsson Pistillate flower abscission of walnut _ 'Serr', 'Sun1and', 'Howard', and 'Chandler'. HortScience 25: Forde, H.I Walnuts, p , In: J. Janick & J.N. Moore (eds.). Advances in fruit breeding. Purdue Univ. Press. Martin, W.F Staining and observing pollen tubes in the style by means of fluorescence. Stain Techno1. 34:

4 Table 1. Pistillate flower abscission at two sites, 1990 Cu1tivar Site l...ffa Serr S 95 UC S 55 UC S 20 UC F 30 UC F 7 Table 2. Pistillate flower abscission of open pollinated and unpo1linated Serr and Chico flowers and after pollination with two dosages of pollen of two. sources. % PFA Treatment Serr Chico Open pollination 93 az 33 a High pollen dose (800 mgfbag) Serr 48 b 19 bc b 20 b Low pollen dose (50 mgfbag) Serr 16 c 11 bc c 6 c Unpo11inated 3 c 12 bc ZMean separation within columns by Duncan's multiple range test, 5% level

5 +:i en -... "(13 '- (!) c: \0 0 f-' 0 IISerrll [ 1-. IiIi Total No" Of Pollen Grains a z r f. Germinated Pollen Grains ~ ~ ~ ~ ~.~ ~ ~ ~ ~ <:\t" 0)' 0)' ~" ~. lr)' lr)" CO" co' ~ " ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Size Class ~ & ~" q," ~ ~ ~ ~ ~" ~. Figure 1. Number of pollen grains per stigma of pistils of increasing ovary diameter (mm). PFA pistils are smaller than mm diameter.

6 I 500 (1j E "2> 400 en - ēn c: "~ 300 (!) c: Q) o 200 a.. o o 100 z..chico.. ii Total No. Of Pollen Grains. Germinated Pollen Grains \D N o ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~. ~. '\)ro. '\)ro. <0. <0. co. co. ". ". Cb" ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ tv" ~. ~. '\)ro. '\)ro. ~. ~. «). «). "" ". Size Class Figure 2. Number of pollen grains per stigma of pistils of increasing ovary diameter (mm). PFA pistils are smaller than mm diameter.